Method and circuit for reducing quantizer input/output swing in a sigma-delta modulator

Abstract

Disclosed is a circuit and method for reducing output swing in a sigma delta modulator. The quantizer output swing reduction circuit and method of the present invention advantageously enables the modulator to have a larger input / output swing range without degrading the SNR and SFDR performance. One embodiment of the present invention comprises a conventional sigma-delta modulation circuit (100) and a quantizer swing reduction block (210). The quantizer swing reduction block (210) comprises an input signal Vx (216), a signal processing block (214) with transfer function H3 and another signal processing block (215) with transfer function H2*H3.

Description

TECHNICAL FIELD[0001]The present invention relates to sigma-delta, sometimes referred to as delta-sigma, modulators used in analog-to-digital converter circuits, specifically a circuit and method for reducing the quantizer input / output swing in a sigma-delta modulator which enables the modulator to have a larger input / output signal swing before the signal at the input / output of the quantizer and the output of the last integrator saturates.BACKGROUND OF THE INVENTION[0002]Most signals of practical interest, such as speech, radar signals, sonar signals and various communication signals such as audio and video signals are analog. Often it is desirable to process these analog signals by digital means. To process an analog signal by digital means, it is necessary to convert the analog signal into digital form.[0003]In analog-to-digital conversion, a smooth and continuous analog signal is converted or quantized into a sequence of numbers having finite precision with discrete values at dis...

AI Technical Summary

Benefits of technology

[0008]The present invention achieves technical advantages as a circuit arrangement and method by which the input / output swing of the quantizer in the sigma-delta modulator is reduced or kept within the limit of the finite quantization levels. Advantageously, the quantizer output swing reduction circuit and method of the present invention enables the modulator to have a larger input / output swing range without degrading the SNR and SFDR performance due to quantizer saturation and clipping.

[0009]A gradually increasing signal introduced into an A / D converter using the circuit and method of the present invention will not clip or saturate at the output of the quantizer as compared to a conventional sigma-delta modulator. Therefore, the circuit and method avoids large signal clipping that causes harmonic distortion and tones which increase the noise floor in the in-band frequency spectrum.

Problems solved by technology

The error between the modulator analog input signal and the modulator digital output code due to the quantizer is the quantization noise

Disadvantageously, sampling frequency is limited by the capability of the device and silicon process technology.

One of the architectural limitations for SNR and spurious-free-dynamic range (“SFDR”) degradation with increasing input signal swing is due to the maximum signal swing limitation.

The maximum signal swing limitation in a quantizer is due to the finite quantization level or the 0 dB full-scale range of the A / D converter.

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